A US company has created a punctuation mark that it hopes will be used to express sarcasm. It can be downloaded for a small charge and then inserted into documents with a Ctrl key command. The company proposes that the SarcMark can be used to avoid confusion in emails:

Anyone concerned that the irony of their email or text message might not be appreciated by its recipient can use the symbol to close their sentence, thereby avoiding awkward misunderstandings.

The symbol – a dot inside a single spiral line – can be installed onto any PC running Windows 7, XP or Vista, as well as Macs and Blackberry mobile devices.

That can't possibly catch on. Bad design. It looks too much like the @ symbol and when hand written will always be confused for that. Also a bad idea to place a dot so close to the lines. A dot works on letters where it is clearly separate from the rest of the letter (i,j) Try to put a dot in the middle of an m and you`re asking for trouble.